(1) Field of the Invention
The invention relates to an outlet air muffler for portable air-powered driving tools, made up of an outlet air duct arrangement, which is formed by the housing end and top lid of the driving tool, which interconnects the outlet side of the main control valve and the outside air.
(2) The Prior Art
Air-powered driving tools are normally worked with, generally speaking, high pressures of 6 to 8.5 bar. The compressed air is let into a cylinder space by control valves so that the working piston is axially moved and a driving rod, fixed to the bottom side of the working piston, has the effect of driving a fixing part (a staple or nail) out of the outlet duct into a workpiece. In the further working operation of this sort of tool, the main and control valves are operated so that the working compressed air in the working pressure space is responsible for moving the working piston between the driving and driven positions and high pressure air is subsequently exhausted into the outside air. On the exhausting of the compressed air, turbulence is produced and with it high frequency noise damaging to the ear. For putting an end to such noise or decreasing it, new designs of compressed air tools have been made with outlet mufflers having the purpose of so decreasing the air speed that no noise damaging to the ear is produced.
Outlet air mufflers have been put forward for air-powered driving tools that are limited in operation because such air-powered driving tools, to be portable handworked tools, are limited in their design size. So more special use has been made of diffusion mufflers which are mainly made up of tightly packed sintered material, plastics, bronze or steel wool. These diffusion mufflers have however the important shortcomings that they are readily put out of order by dirt which makes for a narrowing of the air cross sections as time goes on and for this reason the outlet air speed and furthermore the backward speed of the working piston is steadily decreased. These mufflers seem to be especially likely to be put out of order when used with wet air and, more especially, in cold seasons of the year, because ice is formed with the high air speeds, this having the same braking effect whose outcome may be that the tool may no longer be used. Furthermore, in some cases there will be danger to the user because under the high pressure, parts of the sintered metal will be violently broken off possibly wounding nearby persons. Furthermore, reflection mufflers have been designed, which however have not so far been used for a compressed air plant, because to get a good muffling effect, they have to be such a large size that they are not able to be used with portable plants.